The heart muscle is nourished by blood flow through coronary arteries. These arteries are quite small, but are vital for carrying the blood flow required to maintain the heart in a healthy condition. A predisposing cause of coronary disease is the accumulation of atherosclerotic plaques on the interior walls of the coronary arteries, which tends to reduce their effective diameter. When the lumen is sufficiently narrowed, the rate of blood flow therethrough may be so diminished that spontaneous formation of a thrombus or clot occurs. Once a blood clot has begun to form, it extends within minutes into the surrounding blood, as mentioned in U.S. Pat. No. 4,643,186, issued Feb. 17, 1987, in the names of Rosen and Walinsky, and may, effectively block coronary blood flow. Thus, it is important to restore coronary blood flow before thrombosis occurs. Coronary bypass surgery can ameliorate the effects of such blockage, but may be undesirable, in part because it requires invasive surgery.
Balloon angioplasty techniques are less invasive than coronary artery bypass surgery, and have been shown to be effective under some conditions. In general, a balloon angioplasty procedure is performed by obtaining access to the interior of the affected coronary artery, and advancing a deflated balloon to the location of the stenosis. The balloon is inflated by applying fluid pressure through an inflation/deflation ("inflation") lumen of the catheter, to thereby apply balloon pressure tending to expand the lumen of the coronary artery, to thereby press the plaque against the walls of the coronary artery, and to expand the walls of the artery. When the stenotic portion of the lumen of the blood vessel or coronary artery has about the same diameter as adjacent portions which are free from plaque, the procedure may be terminated, the balloon deflated and the catheter removed. It has been observed, as in the article entitled "Perfusion During Coronary Angioplasty," by Rossen, published at pages 103-106 in the June, 1989 issue of Cardio, that increased time with the balloon inflated is associated with an improved result. When the balloon is removed, the artery tends to remain open, allowing for increased blood flow.
The art relating to angioplasty includes many advances, such as the microwave-aided angioplasty described in the above-mentioned Rosen and Walinsky patent, reduced diameters as described in an article entitled "The Balloon On A Wire Device" by Myler et al, published at pages 135-140 of Volume 14, Nov. 2, 1988 of the periodical "Catheterization and Cardiovascular Diagnosis," published by Alan R. Liss, and various configurations of guide wires and catheter lumens, described for example in "Selection or Dilatation Hardware for PCTA-1985" by Topol et al., published at pages 629-637 of Volume 11, Nov. 6, 1985 of the aforementioned periodical.
Those portions of the heart muscle supplied with blood flow through the artery being treated during balloon angioplasty are partially deprived of blood flow when the catheter with deflated balloon is being positioned in the stenotic region, and may be completely deprived of blood flow when the balloon is inflated. This in turn has a tendency to decrease heart pumping efficiency, and the blood pressure tends to drop. Chest pains result in some patients. Either of these indications may undesirably require early termination of the procedure. Dilatation catheters are available, as mentioned in the above-mentioned Rossen article, in which perfusion or blood flow past the occluding catheter and balloon is provided by fenestrations or apertures into the distal lumen of the catheter on both sides of the balloon. When the distal lumen is also used for a guide wire, as in U.S. Pat. No. 4,762,129, issued Aug. 9, 1988 in the name of Bonzel, and in U.S. Pat. No. 4,994,745, issued Jul. 31, 1990, in the name of Sogard et al., the guide wire blocks at least a portion of the perfusion channel, and must be retracted during perfusion. This retraction requires additional manipulation, and may result in loss of position of the balloon. Further manipulation is required if the guide catheter surrounding the dilatation catheter must also be retracted. Such perfusion catheters tend to be somewhat larger in diameter and stiffer than conventional catheters having the same inflated balloon diameter, and are therefore more difficult to position. Also, their larger diameter excludes their use in the small arteries into which conventional angioplasty balloon catheters may fit.
Perfusion balloon catheters are described in U.S. Pat. No. 4,909,252, issued Mar. 20, 1990 in the name of Goldberger, and in U.S. Pat. No. 5,108,370, issued Apr. 12, 1992 in the name of Walinsky, in which the perfusion channel extends through the balloon, and the guidewire extends through a separate lumen. These balloon catheters provide a perfusion path which is independent of the guidewire, so that the amount of manipulation is reduced by eliminating the need to remove the guidewire to allow sufficient perfusion during balloon inflation, and reduces the possibility of losing balloon position by the removal of the guide wire.
Differential compliance of the balloon material is described in U.S. patent application Ser. No. 08/279,061, filed Jul. 22, 1994, in the name of Walinsky. The differential compliance aids in preventing closure of the perfusion channel extending through the balloon as the balloon is inflated. The differential compliance may require thicker balloon material adjacent the perfusion channel. The various improvements to balloon catheters has tended to increase the diameter of the catheter in the region of the collapsed balloon, which tends to reduce their usefulness in smaller coronary arteries. Improved balloon catheters are desired.